1. Field of the Invention
The present invention relates to a cathode-ray tube electron gun in which unwanted radiation can be reduced and an electron gun having such an cathode-ray tube.
2. Description of the Related Art
Recently, a problem of an unwanted radiation from a cathode-ray tube, in particular, a display monitor driven at a high-frequency voltage, becomes highlighted.
To cope with the unwanted radiation in the display monitor, there is a mainstream that a shield cover is provided to cover the whole of the cathode-ray tube so that unwanted radio waves can be prevented from being radiated to the outside of the cathode-ray tube. Accordingly, there is no technology in which a generation source itself of radio waves generated from a cathode-ray tube is analyzed and a fundamental countermeasure is devised.
When the cathode-ray tube is protected with the large shield cover as described above, it is unavoidable that a manufacturing cost of the cathode-ray tube increases.
On the other hand, the assignee of the present application has analyzed the related-art electron gun, and has discovered an unwanted radiation generation source for an electron gun.
FIG. 1 of the accompanying drawings shows a structure of a typical electron gun for use with a color cathode-ray tube.
As shown in FIG. 1, this electron gun 12 comprises three cathodes KR, KG and KB corresponding to red, green and blue arranged in an inline fashion. A first electrode (G1) 1, a second electrode (G2) 2, a third electrode (G3) 3, a fourth electrode (G4) 4, a fifth electrode (G5) 5, a sixth electrode (G6) 6 are sequentially arranged on the same axis so as to become common to the three cathodes KR, KG and KB. A shield cup 7 is provided at the final stage, and this electron gun is arranged as a so-called unibipotential system three-beam single electron gun. The first electrode 1 and the second electrode 2 are each formed of a plate-like material.
The first electrode 1 is supplied with about 0V from a first electrode lead (electrically-conducting lead) 9, the second electrode 2 and the fourth electrode 4 are supplied with about 200V to 800V from a second electrode lead (electrically-conducting lead) 10 and the third electrode 3 and the fifth electrode 5 are supplied with a focusing voltage of about 20% to 35% of an anode voltage (high voltage) from a focus lead (electrically-conducting lead). The first electrode lead 9, the second electrode lead 10 and the focusing lead 11 are connected to stem pins, respectively. The sixth electrode 6 and the shield cup 7 are supplied with an anode voltage of about 20 kV to 32 kV. The three cathodes KR, KG, KB are driven by a high-frequency voltage (i.e., a so-called video signal).
In this electron gun 1, electron beams BR, BG and BB generated and controlled y the cathodes KR, KG, KB and the first electrode 1 and the second electrode 2 are adjusted in divergence angle by a front-stage electron lens or a front-stage focusing lens comprising the third electrode 3, the fourth electrode 4 and the fifth electrode 5 and then focused by a main electron lens (i.e., a main focusing lens) comprising the fifth electrode 5 and the sixth electrode 6.
FIG. 2 shows a color cathode-ray tube having such electron gun 12.
As shown in FIG. 2, in a color cathode-ray tube 13, the above-mentioned electron gun 12 is disposed within a neck portion 15 of a cathode-ray tube assembly (i.e., a so-called glass bulb) 14 in an opposing relation to a fluorescent screen 17. A color selection mechanism is closely opposed to the fluorescent screen 17, although not shown. Further, there are disposed a deflection yoke 16 outside the cathode-ray tube assembly 14 for deflecting the electron beams BR, BG, BB in the horizontal and vertical directions. In FIG. 2, reference numeral 18 denotes a video base plate disposed on the end portion of the neck portion 15. This color cathode-ray tube 13 is covered at its whole rear portion except the front surface of a panel portion 19 with a shield cover material 20 in order to protect it from the influence of unwanted radiation, a terrestrial magnetism or the like.
In general, the first electrode lead 9 and the second electrode lead 10 of the above-mentioned electron gun 12 are each a single electrode lead because it is intended to supply a voltage for electrically conducting the electron gun 12. In particular, in the case of the plate-like first electrode 1 and second electrode 2, the first electrode lead 9 and the second electrode lead 10 are each a single electrode lead.
FIG. 3 is a schematic diagram showing the first electrode 1 having the cathodes KR, KG, KB and one lead 9 as a model example. In FIG. 3, reference numerals 22 denote electron beam apertures defined in the first electrode 1 to pass electron beams. With this arrangement, when the cathodes KR, KG, KB are driven by a high-frequency voltage, the first electrode 1, which is spaced apart from the cathodes KR, KG, KB by a short distance of about 50 xcexcm to 200 xcexcm has a capacity between it and the cathodes KR, KG, KB, so that the cathodes KR, KG, KB, the first electrode 1 and the first electrode lead 9 constitute a high-efficiency antenna, thereby causing unwanted radiation.
That is, the assignee of the present application has discovered that, when the first electrode lead 9 is the single electrode lead, the cathodes (KR, KG, KB) and the first electrode 1 constitute the high-efficiency antenna which serves as an unwanted radio wave generation source.
This is also considered in the second electrode 2.
FIG. 4 is a schematic diagram showing the first electrode 1 having the cathodes KR, KG, KB and one lead 9 and the second electrode 2 having one lead 10 as a model example. In FIG. 4, reference numerals 23 designate electron beam apertures defined in the second electrode 2 to pass electron beams.
Since the second electrode 2 is spaced apart from the first electrode 1 by a distance of about 0.1 mm to 0.3 mm, although a magnitude of capacity becomes small as compared with that of the first electrode 1, the second electrode has a capacity between it and the cathodes KR, KG, KB to form an antenna to cause unwanted radiation.
Unwanted radiation generated from the electron gun 12 where the first electrode 1 and the second electrode 2 have each single leads 9 and 10 as shown by the model example in FIG. 3 or 4 is represented as shown by a curve I in FIG. 15 which shows unwanted radiation level.
The graph of FIG. 15 shows unwanted radiation level measured by a detection antenna located at the position distant from the electron gun 12 by a distance of 1 m when the high-frequency voltage is applied to the cathodes KR, KG, KB. In the graph of FIG. 15, the vertical axis represents a relative value of unwanted radiation level, and the horizontal axis represents the frequency of the high-frequency voltage applied to the cathodes.
Accordingly, in the color cathode-ray tube 13 having the electron gun 12 which is arranged as shown in FIGS. 3 and 4, the shield cover material 20 shown in FIG. 2 should have a considerably strong shielding effect.
The radio wave generation source itself of the electron gun according to the related art has been described so far.
In view of the results obtained when the above-mentioned radio wave generation source itself was analyzed, it is an object of the present invention to provide a cathode-ray tube electron gun in which unwanted radiation can be alleviated and a cathode-ray tube including such electron gun.
According to the present invention, there is provided a cathode-ray tube electron in which a first electrode includes a plurality of electrical conduction leads.
Since the first electrode includes a plurality of conduction leads, the first electrode can achieve a shield action for the cathode so that unwanted radiation caused by the antenna comprised of the cathode and the first electrode according to the related art can be alleviated.
The cathode-ray tube according to the present invention includes the above-mentioned electron gun, i.e. the electron gun in which the first electrode includes a plurality of electrical conduction leads.
According to the above-mentioned arrangement, unwanted radiation caused in the cathode-ray tube by the antenna comprised of the cathode and the first electrode can be alleviated unlike the related-art electron gun.
According to a cathode-ray tube electron gun of a first embodiment of the invention, a first electrode includes a plurality of electrical conduction leads.
According to a cathode-ray tube electron gun of a second embodiment of the invention, a first electrode includes a plurality of electrical conduction leads and the electrical conduction leads are spaced apart from each other by a distance long enough to produce a shield action for cathodes.
According to a cathode-ray tube electron gun of a third embodiment of the invention, a first electrode includes more than two electrical conduction leads and said respective electrical conduction leads are set in a positional relationship such that a line connecting two points at which at least one set of the opposing two electrical conduction leads exist overlaps with a cathode region or exists near the cathode region as seen from the electrode surface of the first electrode.
According to a cathode-ray tube electron gun of a fourth embodiment of the invention, a first electrode includes more than three electrical conduction leads and the respective electrical conduction leads are set in a position relationship such that a cathode exists in a polygon connecting respective points in which the respective electrical conduction leads exist or sides of the polygon overlap with the cathode region as seen from the electrode surface of the first electrode.
According to a cathode-ray tube of a fifth embodiment of the invention, a second electrode includes a plurality of electrical conduction leads.
According to a cathode-ray tube of a sixth embodiment of the invention, a second electrode includes a plurality of electrical conduction leads and the electrical conduction leads are spaced apart from each other by a distance long enough to produce a shield action for cathodes.
According to a cathode-ray tube of a seventh embodiment of the invention, a second first electrode includes more than two electrical conduction leads and the respective electrical conduction leads are set in a positional relationship such that a line connecting two points at which at least one set of the opposing two electrical conduction leads exist overlaps with a cathode region or exists near said cathode region as seen from the electrode surface of the first electrode.
According to a cathode-ray tube of an eighth embodiment of the invention, a second electrode includes more than three electrical conduction leads and the respective electrical conduction leads are set in a position relationship such that a cathode exists in a polygon connecting respective points in which the respective electrical conduction leads exist or sides of the polygon overlap with the cathode region as seen from the electrode surface of the second electrode.
According to a cathode-ray tube of a ninth embodiment of the invention, in the cathode-ray tube electron gun according to the first embodiment, the second electrode includes a plurality of electrical conduction leads.
According to a cathode-ray tube of a tenth embodiment of the invention, in the cathode-ray tube electron gun according to the first embodiment, the second electrode includes a plurality of electrical conduction leads and the electrical conduction leads are spaced apart from each other by a distance long enough to produce a shield action for cathodes.
According to a cathode-ray tube of an eleventh embodiment of the invention, in the cathode-ray tube electron gun according to the first embodiment, the second electrode includes more than two electrical conduction leads and the respective electrical conduction leads are set in a positional relationship such that a line connecting two points at which at least one set of the opposing two electrical conduction leads exist overlaps with a cathode region or exists near the cathode region as seen from the electrode surface of the first electrode.
According to a cathode-ray tube electron gun of a twelfth invention, in the cathode-ray tube electron gun according to the first embodiment, the second electrode includes more than three electrical conduction leads and said respective electrical conduction leads are set in a position relationship such that a cathode exists in a polygon connecting respective points in which the respective electrical conduction leads exist or sides of the polygon overlap with the cathode region as seen from the electrode surface of the second electrode.
According to a cathode-ray tube electron gun of a thirteenth embodiment of the invention, in the cathode-ray tube electron gun according to the second embodiment, the second electrode includes a plurality of electrical conduction leads.
According to a cathode-ray tube electron gun of a fourteenth embodiment of the invention, in the cathode-ray tube electron gun according to the second embodiment, the second electrode includes a plurality of electrical conduction leads and the electrical conduction leads are spaced apart from each other by a distance long enough to produce a shield action for cathodes.
According to a cathode-ray tube electron gun of a fifteenth embodiment of the invention, in the cathode-ray tube electron gun according to the second embodiment, the second first electrode includes more than two electrical conduction leads and said respective electrical conduction leads are set in a positional relationship such that a line connecting two points at which at least one set of the opposing two electrical conduction leads exist overlaps with a cathode region or exists near the cathode region as seen from the electrode surface of the second electrode.
According to a cathode-ray tube electron gun of a sixteenth embodiment of the invention, in the cathode-ray tube electron gun according to a third embodiment, the second electrode includes more than three electrical conduction leads and the respective electrical conduction leads are set in a position relationship such that a cathode exists in a polygon connecting respective points in which the respective electrical conduction leads exist or sides of the polygon overlap with the cathode region as seen from the electrode surface of the second electrode.
According to a cathode-ray tube electron gun of a seventeenth embodiment of the invention, in the cathode-ray tube electron gun according to the third embodiment, the second electrode includes a plurality of electrical conduction leads.
According to a cathode-ray tube electron gun of an eighteenth embodiment of the invention, in the cathode-ray tube electron gun according to the third embodiment, the second electrode includes a plurality of electrical conduction leads and the electrical conduction leads are spaced apart from each other by a distance long enough to produce a shield action for cathodes.
According to a cathode-ray tube electron gun of nineteenth embodiment of the invention, in the cathode-ray tube electron gun according to the third embodiment, the second electrode includes more than two electrical conduction leads and the respective electrical conduction leads are set in a positional relationship such that a line connecting two points at which at least one set of the opposing two electrical conduction leads exist overlaps with a cathode region or exists near the cathode region as seen from the electrode surface of the second electrode.
According to a cathode-ray tube electron gun of a twentieth embodiment of the invention, in the cathode-ray tube electron gun according to the third embodiment, the second electrode includes more than three electrical conduction leads and the respective electrical conduction leads are set in a position relationship such that a cathode exists in a polygon connecting respective points in which the respective electrical conduction leads exist or sides of the polygon overlap with the cathode region as seen from the electrode surface of the second electrode.
According to a cathode-ray tube electron gun of a twenty-first embodiment of the invention, in the cathode-ray tube electron gun according to the fourth embodiment, the second electrode includes a plurality of electrical conduction leads.
According to a cathode-ray tube electron gun of a twenty-second embodiment of the invention, in the cathode-ray tube electron gun according to the fourth embodiment, the second electrode includes a plurality of electrical conduction leads and the electrical conduction leads are spaced apart from each other by a distance long enough to produce a shield action for cathodes.
According to a cathode-ray tube electron gun of a twenty-third embodiment of the invention, in the cathode-ray tube electron gun according,to the fourth embodiment, the second first electrode includes more than two electrical conduction leads and the respective electrical conduction leads are set in a positional relationship such that a line connecting two points at which at least one set of the opposing two electrical conduction leads exist overlaps with a cathode region or exists near the cathode region as seen from the electrode surface of the second electrode.
According to a cathode-ray tube electron gun of a twenty-fourth embodiment of the invention, in the cathode-ray tube electron gun according to the fourth embodiment, the second electrode includes more than three electrical conduction leads and the respective electrical conduction leads are set in a position relationship such that a cathode exists in a polygon connecting respective points in which the respective electrical conduction leads exist or sides of the polygon overlap with the cathode region as seen from the electrode surface of the second electrode.
A cathode-ray tube according to a twenty-fifth embodiment of the invention includes an electron gun of the first embodiment.
A cathode-ray tube according to a twenty-sixth embodiment of the invention includes an electron gun of the fifth embodiment.
A cathode-ray tube according to a twenty-eighth invention includes an electron gun of the ninth embodiment.